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• FFMPEG : How to avoid audio/video desync in output of crossfaded clips when input is variable frame rate video

  25 décembre 2018, par Anders Lunde

  I’m doing screen recordings of gameplay (Dota2) using my NVIDIA graphics card GeForce experience hardware recording (NVEC Encoder). This creates a variable frame rate output video. My NVIDIA settings are 60 fps 15000 kbps. I have paid a guy to make a program that generates scripts that given start/stop timepoints can extract clips from the video and merge them with crossfade. See example code below. The script works for many input recordings but fails often : The audio and video are desynchronized (usually audio delay) in many of the clips, ca 0.5 seconds. I think it fails more when frame rate dropped more during recording. He does not know how to fix the problem, and I wonder if anyone could point out if anything could be fixed in the script (example below) ?

  Processing speed is quite important (now making a 10 min ’highlight’ video takes ca 7-10 min). Solutions increasing that amount very much more is not of too big interest, unfortunately. His approach has been to work separately with audio and video and merge in the end. He already has a program to make ffmpeg code for working with different scenarios (also adding overlays, adding music, intro/outro) so it would be preferable with some easy fixes to his code and not dramatic redesigning of the logic. But if nothing else can fix the problem, a redesign in logic is ok. Using other tools than ffmpeg is also ok, but should be automatable (scripts/cli) and not increase processing times too much.

  Running the program "mediainfo" on the input video shows that framerate dropped quite low for this input video :

  Frame rate mode : Variable

  Frame rate : 60.000 FPS

  Minimum frame rate : 3.059 FPS

  Maximum frame rate : 63.739 FPS

  Full report here : https://pastebin.com/TX061Wih

  The input video can be downloaded from dropbox here (6 GB) :
  https://www.dropbox.com/s/ftwdgapazbi62pr/fullgame.mp4?dl=0

  Here the example of a script when asked to extract two clips from input video at 9:57 (41 sec length) and 15:45 (28 sec length) and crossfade merge them with a 0.5 crossfade time. There might be some code-remnants from options that are not used in this example (overlays, music, intro/outro). Using the input video above, this creates audio/video desync.

  6 commands excecuted in sequence :

  ffmpeg.exe -loglevel warning -ss 00:09:57 -i fullgame.mp4 -t 00:00:41 -filter_complex "[0:a]afade=t=out:st=40.5:d=0.5[a1]" -map "[a1]" -y out_temp_00.mp4.wav
  
  
  
  ffmpeg.exe -loglevel warning -i fullgame.mp4 -ss 00:09:57 -t 00:00:41 -an -vcodec copy -f mpegts -avoid_negative_ts make_zero -y out_temp_00.mp4.ts
  
  
  
  ffmpeg.exe -loglevel warning -ss 00:15:45 -i fullgame.mp4 -t 00:00:28 -filter_complex "[0:a]afade=t=in:st=0:d=0.5[a1]" -map "[a1]" -y out_temp_01.mp4.wav
  
  
  
  ffmpeg.exe -loglevel warning -i fullgame.mp4 -ss 00:15:45 -t 00:00:28 -an -vcodec copy -f mpegts -avoid_negative_ts make_zero -y out_temp_01.mp4.ts
  
  
  
  ffmpeg.exe -loglevel warning -i out_temp_00.mp4.wav -i out_temp_01.mp4.wav -y -filter_complex "[0:a]adelay=0|0[a0];[1:a]adelay=40500|40500[a1];[a0][a1]amix=inputs=2:dropout_transition=68.5,atrim=duration=68.5[outa0];[outa0]loudnorm[outa]" -map "[outa]" -ar 48000 -acodec aac -strict -2 fullgame_Output.mp4.aac
  
  
  
  ffmpeg.exe -loglevel warning -i out_temp_00.mp4.ts -i out_temp_01.mp4.ts -y -i fullgame_Output.mp4.aac  -filter_complex "[0:v]trim=start=0.5,setpts=PTS-STARTPTS[0c];[1:v]trim=start=0.5,setpts=PTS-STARTPTS[1c];[0:v]trim=40.5:41,setpts=PTS-STARTPTS[fo];[1:v]trim=0:0.5[fi];[fi]format=pix_fmts=yuva420p,fade=t=in:st=0:d=0.5:alpha=1[z];[fo]format=pix_fmts=yuva420p,fade=t=out:st=0:d=0.5:alpha=1[x];[z]fifo[w];[x]fifo[q];[q][w]overlay[r];[0c][r][1c]concat=n=3[outv]" -map "[outv]" -map 2:a -shortest -acodec copy -vcodec libx264 -preset ultrafast -b 15000k -aspect 1920:1080 fullgame_Output.mp4

  P.S.

  I already asked for help at an ffmpeg chat room. One guy said he knew what the problem was, but didnt know how to fix it(?) :

  [00:10] <kepstin> oh, wait, you're using -vcodec copy
  
  [00:10] <kepstin> that explains everything.
  
  [00:10] <kepstin> when you're using -vcodec copy, the start time (set with -ss) is rounded to the nearest keyframe
  
  [00:10] <kepstin> it's not exact
  
  [00:11] <kepstin> depending on the keyframe interval, this will result in possibly quite large shifts
  
  [00:11] <kepstin> (also, your commands are applying audio filters on commands with -an, which is confusing/contradictory)
  
  [00:12] <birdboy88> so the problem is that the audio temporary clips are not being extracted from the same excat timepoints?
  
  [00:13] <kepstin> birdboy88: yeah, your audio is being re-encoded to wav so it's being cut sample-accurate, but the video's not being precisely cut.
  
  [00:16] <birdboy88> kepstin: so I need to use slow seek (?) to extract video accurately? Or somehow extract audio only where there are video keyframes?
  
  [00:17] <kepstin> birdboy88: i don't know how to extract audio starting at video keyframes with ffmpeg cli. You're already doing slow seek, which doesn't help (you should move the -ss option to before the -i option to speed it up)
  
  [00:17] <kepstin> if you want accurate video cutting when saving to a file, you have to re-encode the video
  
  [00:18] <kepstin> (doing this in a single ffmpeg command means you don't have to save to a file, so you can avoid the issue)
  
  [00:18] * kepstin is off for a bit now
  
  </kepstin></kepstin></kepstin></birdboy88></kepstin></birdboy88></kepstin></kepstin></kepstin></kepstin></kepstin></kepstin>

  EDIT :
  Everything is done with the latest ffmpeg version.

  I was unable to get Gyan’s code to work. It always loses some audio (audio is either 40.5 or 27.5, so only one audio is used). This is the only one working for me (changes were adelay=40500|40500 and amix=inputs=2[a0] ;[a0]loudnorm) :

  ffmpeg -i fullgame.mp4 -filter_complex "[0]split=2[vpre][vpost];
  
  [0]asplit=2[apre][apost];
  
  [vpre]trim=start='00:09:57':duration='00:00:41',setpts=PTS-STARTPTS[vpre-t];
  
  [apre]atrim=start='00:09:57':duration='00:00:41',asetpts=PTS-STARTPTS,afade=t=out:st=40.5:d=0.5[apre-t];
  
  [vpost]trim=start='00:15:45':duration='00:00:28',setpts=PTS-STARTPTS,format=yuva420p,fade=t=in:st=0:d=0.5:alpha=1,setpts=PTS+40.5/TB[vpost-t];
  
  [apost]atrim=start='00:15:45':duration='00:00:28',asetpts=PTS-STARTPTS,afade=t=in:st=0:d=0.5,adelay=40500|40500[apost-t];
  
  [vpre-t][vpost-t]overlay[v];
  
  [apre-t][apost-t]amix=inputs=2[a0];[a0]loudnorm[a]" -map "[v]" -map "[a]" -y -c:v libx264 -preset ultrafast -b:v 15000k -aspect 1920:1080 -c:a aac fullgame_Output.mp4

  Then I tried using a similar setup but with 3 clips, but on one machine I got error : "Error while filtering : Cannot allocate memory". And my 16 GB memory machine the processing speed is 0.02x ! Any way to avoid this ? This is the code I tried :

  ffmpeg -i fullgame.mp4 -filter_complex "[0]split=3[vpre][vpost][v3];
  
  [0]asplit=3[apre][apost][a3];
  
  [vpre]trim=start=357:duration=41,setpts=PTS-STARTPTS[vpre-t];
  
  [apre]atrim=start=357:duration=41,asetpts=PTS-STARTPTS,afade=t=out:st=40.5:d=0.5[apre-t];
  
  [vpost]trim=start=795:duration=28,setpts=PTS-STARTPTS,format=yuva420p,fade=t=in:st=0:d=0.5:alpha=1,fade=t=out:st=40.5:d=0.5:alpha=1,setpts=PTS+40.5/TB[vpost-t];
  
  [apost]atrim=start=795:duration=28,asetpts=PTS-STARTPTS,afade=t=in:st=0:d=0.5,afade=t=out:st=27.5:d=0.5,adelay=40500|40500[apost-t];
  
  [v3]trim=start=95:duration=30,setpts=PTS-STARTPTS,format=yuva420p,fade=t=in:st=0:d=0.5,setpts=PTS+41Û0.5/TB[v3-t];
  
  [a3]atrim=start=95:duration=30,asetpts=PTS-STARTPTS,afade=t=in:st=0:d=0.5,adelay=68500|68500[a3-t];
  
  [vpre-t][vpost-t]overlay[v1];
  
  [v1][v3-t]overlay[v];
  
  [apre-t][apost-t][a3-t]amix=inputs=3[a0];
  
  [a0]loudnorm[a]" -map "[v]" -map "[a]" -y -c:v libx264 -preset ultrafast -b:v 15000k -aspect 1920:1080 -c:a aac fullgame_Output.mp4

• How to keep personally identifiable information safe

  23 janvier 2020, par Joselyn Khor
  The protection of personally identifiable information (PII) is important both for individuals, whose privacy may be compromised, and for businesses that may have their reputation ruined or be liable if PII is wrongly accessed, used, or shared.

  Curious about what PII is ? Here’s your introduction to personally identifiable information.

  Due to hacking, data leaks or data thievery, PII acquired can be combined with other pieces of information to form a more complete picture of you. On an individual level, this puts you at risk of identity theft, credit card theft or other harm caused by the fraudulent use of your personal information.

  On a business level, for companies who breach data privacy laws – like Cambridge Analytica’s harvesting of millions of FB profiles – the action leads to an erosion of trust. It can also impact your financial position as heavy fines can be imposed for the illegal use and processing of personally identifiable information.

  So what can you do to ensure PII compliance ?

  On an individual level :

  1. Don’t give your data away so easily. Although long, it’s worthwhile to read through privacy policies to make sure you know what you’re getting yourself into.
  2. Don’t just click ‘agree’ when faced with consent screens, as consent screens are majorly flawed. Users mostly always opt in without reading and without being properly informed what they opt in to.
  3. Did you know you’re most likely being tracked from website to website ? For example, Google can identify you across visits and websites. One of the things you can do is to disable third party cookies by default. Businesses can also use privacy friendly analytics which halt such tracking. 
  4. Use strong passwords.
  5. Be wary of public wifi – hackers can easily access your PII or sensitive data. Use a VPN (virtual private network), which lets you create a secure connection to a server of your choosing. This allows you to browse the internet in a safe manner.

  A PII compliance checklist for businesses/organisations :

  1. Identify where all PII exists and is stored – review and make sure this is in a safe environment.
  2. Identify laws that apply to you (GDPR, California privacy law, HIPAA) and follow your legal obligations.
  3. Create operational safeguards – policies and procedures for handling PII at an organisation level ; and building awareness to focus on the protection of PII.
  4. Encrypt databases and repositories where such info is kept.
  5. Create privacy-specific safeguards in the way your organisation collects, maintains, uses, and disseminates data so you protect the confidentiality of the data.
  6. Minimise the use, collection, and retention of PII – only collect and keep PII if it’s necessary for you to perform your legal business function.
  7. Conduct privacy impact assessments (PIA) to find and prevent privacy risks (identify what and why it’s to be collected ; how the information will be secured etc.).
  8. De-identify within the scope of your data collection and analytics tools.
  9. Anonymise data.
  10. Keep your privacy policy updated.
  11. Pseudonymisation.
  12. A more comprehensive guide for businesses can be found here : https://iapp.org/media/pdf/knowledge_center/NIST_Protecting_PII.pdf

  Unsure of what information could be considered PII ? Check out this list of examples.

  Additional resources :

  • https://www.umassmed.edu/it/security/compliance/what-is-pii/
  • http://www.osec.doc.gov/opog/privacy/PII_BII.html

• create multiple movie thumbnails using ffmpeg (one at a time) failing

  2 septembre 2013, par Christopher Johnson

  I'm using this small bit of code to create thumbnails of videos being uploaded to my site :

  public static void GetThumbnail(string video, string thumbnail)
  
  {
  
      var cmd = "ffmpeg  -itsoffset -1  -i " + '"' + video + '"' + " -vcodec mjpeg -vframes 1 -an -f rawvideo -s 320x240 " + '"' + thumbnail + '"';
  
      var startInfo = new ProcessStartInfo
  
      {
  
          WindowStyle = ProcessWindowStyle.Hidden,
  
          FileName = "cmd.exe",
  
          Arguments = "/C " + cmd
  
      };
  
  
  
      var process = new Process
  
      {
  
          StartInfo = startInfo
  
      };
  
  
  
      process.Start();
  
  }

  I'm uploading the videos one at a time asynchronously. The first video thumbnail gets created just fine, but each subsequent one does not get created. I've noticed that if I try to delete subsequent videos from the file system, it says it can not delete them because they are in use by ffmpeg. I can delete the first one that finished processing just fine. I have to kill the ffmpeg process from task manager for all of the others that it's holding open. Why is ffmpeg only working the first time through and then holding the video's open in an open process afterwards ?

  I also tried creating multiple thumbnails one at a time from the command prompt and that worked fine (the process does not stay open either).

  What am I missing in my c# code to make sure the process finishes, and then terminates ?